Field of the Invention
The invention relates to a motor vehicle control device having a controller as a component of a control loop for controlling the electric current of an actuator, wherein the electrical system voltage of a motor vehicle voltage source is applied to the actuator.
For e.g. a transmission, in particular an automatic transmission, in a motor vehicle, a coupling for selecting and shifting gears is hydraulically actuated as a hydraulic device. Other hydraulic devices used in a motor vehicle are also, for example, brakes for linking or locking shafts or pressure controllers for fuel injection systems, the hydraulic actuation of the particular hydraulic device taking place such that, in the latter, the flow rate for a hydraulic medium, in particular a fluid, and therefore its hydraulic pressure are set by at least one actuator, in particular a so-called solenoid control valve, using a preferably digital control loop. The flow rate for the fluid through e.g. a solenoid control valve as an actuator is dependent on the coil current flowing through the valve and is adjusted by a current controller. For this purpose there is provided in the feedback path of the control loop a sensing element or sensor with the aid of which the actual current through the solenoid control valve is determined and fed to the input of the preferably digital controller, in particular a PID controller. On the basis of a stored set of characteristics of the solenoid control valve, the hydraulic pressure of the hydraulic medium in the hydraulic device to be actuated can be inferred from the measured current through the solenoid control valve.
In practice, a motor vehicle's on-board electrical system voltage or supply voltage may be unstable. In particular, various factors can cause it to fluctuate by as much as several volts. These fluctuations in the vehicle's electrical system supply voltage may also be transmitted to the current flowing through the respective actuator for the hydraulic device, in particular through the respective solenoid control valve, resulting in disturbances being applied to the controlled variable of this control loop. The control loop reacts to these disturbances with corrective action, so that these disturbances cannot be corrected again by the controller until after a particular time interval. This means that in practice the setting and maintaining of a particular desired current value for the actuator, in particular a coil current value for the solenoid valve, preferably a solenoid control valve, is impaired or made more difficult. In particular, unfavorable periodic frequencies (resonant frequencies) of the coil current disturbances caused by vehicle electrical system supply voltage fluctuations may result in unwanted oscillation or even resonance of the actual current, i.e. the output-side controlled variable of the current controller or actuator. This can even lead to instability of the control loop.
In the case of the digital control loop of JP 072 295 76 A, to control the current of a solenoid valve on the basis of battery voltage changes, the integration constant and the proportionality constant of the controller of said digital control loop are changed with the aid of controller parameter values stored in a table. Adjustment of the controller parameters is possible to limited extent, i.e. in more or less large steps, depending on the size of the table. However, a disturbance in the controlled current of the solenoid control valve in the event of any sudden unwanted change in the vehicle's electrical system voltage may still occur. This previous attempt to counteract any vehicle electrical system voltage fluctuations merely by variably adjusting the controller parameters such as KP, KI, KD of the controller e.g. by software or hardware does not prevent the controller from still attempting to correct disturbances in its deviation signal caused by fluctuations in the vehicle electrical system voltage. Moreover, a parameter set optimized for very low battery voltages could result in unwanted effects, particularly even in instabilities, if the battery voltage quite suddenly increases unexpectedly and unintentionally. In terms of the controller parameters, this approach therefore requires a compromise in their selection in order to ensure sufficient stability. However, this is at the expense of the dynamic response and therefore the performance and convenience of the control loop.
For improved setting of the electrical current of an actuator, the object of the invention is to provide a motor vehicle control device having a controller as a component of a control loop, said control device being largely robust to fluctuations in the vehicle electrical system supply voltage.